I dunno if the show made it that clear: is it the Mane 7 ruling Equestria together, like all 7 of them are leaders, or is it Twilight ruling it and the friends just assisting her but she has the final say?
It hasn't been made clear yet, but I've assumed it's the latter. Maybe we'll find out more before the series ends – I wouldn't be surprised to see the rest of them get some (official) royal duties, even if Twilight is the ruler.